Upon tapping, molten iron and molten slag produced in the furnace bottom of a blast furnace are discharged from a molten iron taphole to a molten iron runner. According to a prior art tapping, although the diameter of a molten iron taphole is small at the beginning of tapping, the bore (cross-section) of the molten iron taphole is increased with the progress of the tapping, and the discharge rates of molten iron and molten slag are acceleratedly increased. As a result, in the tapping process, the discharge rates of molten iron and molten slag get ahead of the production rates of molten iron and molten slag, and thereby the surfaces of molten iron and molten slag stored in the furnace bottom are lowered. As the surface levels of molten iron and molten slag stored in the furnace bottom are lowered with the increased discharge amounts thereof and the upper surface level of molten slag reaches the inner level of the molten iron taphole, a furnace gas comes to be jetted from the molten iron hole, thus making is difficult to continue the discharge of molten iron and molten slag. In such a stage, the molten iron taphole is blocked for completing the tapping, and another molten iron taphole is drilled, to thus starting the subsequent tapping. Conventionally, the tapping time using one molten iron taphole is in the range of from 2 to 4 hours, and at this time interval, the tapping is alternately performed using a pair of molten iron tapholes.
The tapping works according to the prior art has the following disadvantages:
(1) The tapping works include extremely heavy works such as a work for drilling or blocking a molten iron taphole; a work for repairing an molten iron runner or a molten slag runner; and a preliminary work for repeated tapping. These tapping works are expected to be reduced; however, the tapping time through one molten iron taphole is limited to 2 to 4 hours due to wear of mud, and accordingly a pair of molten iron tapholes must be alternately used. As a result, two groups of operators must be engaged in the tapping works, thus obstructing the labor-saving.
(2) A molten iron preliminary treating equipment in a casting bed and a slag granulating treating equipment for processing molten slag require the equipment abilities corresponding to the maximum values of molten iron and molten slag at the end of tapping, which are excessively large as compared with the average abilities.
(3) Since the discharge rates of molten iron and molten slag can be adjusted only by changing the diameter of a drill or a metal bar used for drilling a molten iron taphole, they are determined depending on the wear amount of mud forming the molten iron taphole. Consequently, when the discharge rates of molten iron and molten slag are excessively low, the surface levels of molten iron and molten slag in the furnace are abnormally increased, thus leading to instable operation. On the contrary, when the discharge rates thereof are excessively high, there arise troubles due to the lack of processing abilities in a molten iron preliminary treatment, slag granulating treatment, and the like.
(4) In the tapping works using a drill-tapper and mud gun, there arises 5 to 10% of the percent defective in drilling and in drying of mud even using highly mechanized drill-tapper and mud gun, to cause non-steady works, thus making it further difficult to achieve the labor-saving for the tapping work.
(5) Since the tapping works are performed in a batch process using two molten iron tapholes, a variation in quality of molten iron such as a molten iron temperature and the composition of molten iron is large, thus causing an inconvenience in works of a molten iron preliminary treatment performed between an iron-making section and steel-making section.